Survey monuments which must be driven deep underground or to an indeterminate point of refusal commonly include several sections of rod which are joined as the monument is installed. After the monument has been fully driven, a marker cap, designed to fit tightly over the monument, is affixed to the top of the uppermost rod.
A particularly useful monument is disclosed by U.S. Pat. No. 4,087,945 to Berntsen, et al. The Berntsen, et al. monument has cylindrical rods which are joined by threaded connectors incorporated within the cylindrical cross-section of the rods and a barbed penetrating point designed to rotate as it is driven such that the threaded connections are tightened during the driving process. Devices incorporating the self-tightening invention disclosed by Berntsen, et al. are relatively easy to install.
Finned monument rods adapted to be driven through the ground are also known as shown in U.S. Pat. No. 4,502,258 to Rushing. Such rods offer rotational and horizontal stability once in place and are thus particularly appropriate for use as survey monuments. Finned rods, however, are generally more resistant to being driven than cylindrical rods and, of course, cannot be used where they must rotate during installation. Moreover, capping a finned rod at the ground surface can be inhibited by the fins. Also, standard marker caps designed for monuments of standard cross-section, particularly cylindrical monuments, cannot be used on the finned sections unless the fins are first severed and the remaining rod is filed down to permit capping. This can prove cumbersome in the field, particularly where the process must be accomplished at or slightly below ground grade.
One type of finned survey monument is disclosed in U.S. Pat. No. 4,625,473, issued Dec. 2, 1986, to Peterson, et al. This patent discloses an anti-twist rod section having at least one fin attached thereon. The fin is attached along a groove so that it may be removed from the anti-twist rod section if desired. The finned sections disclosed by Peterson, et al. are formed as part of the uppermost rod section. Therefore, one must know in advance when to attach the section having the fins. This is not always possible when the monument reaches a point of refusal. Also, because the fins are comprised of metal, the are heavy and difficult to carry into the field. Moreover, being comprised of metal the removal of the fins from the rod section is not always easy.